For almost 17 years, he had eluded the most brilliant criminal investigators, while continuing to send death through the mails in the form of packages addressed to unsuspecting recipients. Despite a $1-million bounty on his head, the so-called Unabomber named for his penchant for sending the mail bombs to employees of universities, airlines and other corporations apparently had no problem concealing his identity.

The serial bomber, whose lethal handiwork has been blamed for three deaths and millions of dollars in property damage, was known to the public only as an eerie-looking sketch of a mustachioed man wearing a hooded sweatshirt and oversized, aviator-style sunglasses.

The sketch by Jeanne Boylan, one of the nation’s leading forensic artists, was based on the description of a woman who worked at a Salt Lake City computer store where the hooded man left a camouflaged bomb that exploded in 1987, injuring the store’s owner. That was the closest law enforcement ever came to snaring the Unabomber, who must have realized how close he came to being caught: He didn’t strike again for six years.

All of that changed on April 3, when scores of Federal agents converged on a rickety 10-by-12-foot wooden cabin near Lincoln, Mont., and after a brief struggle, emerged with Theodore Kaczynski, 53, the man now charged in at least four of the 16 package and mail bombs attributed to the Unabomber since 1978. Kaczynski, who has pleaded not guilty to the few Unabomber-related cases for which he has been charged, is to be tried in the first case next November in Sacramento, Calif.

Kaczynski’s bearded, unkempt appearance suggested an austere existence, and indeed, the Harvard-educated, mathematics genius who once taught at Berkeley had lived for 25 years as an impoverished hermit in the shack, which had no running water, indoor plumbing or electricity. There, Kaczynski, a native of suburban Chicago, hunted animals for food, grew his own vegetables and sometimes spent entire winters sequestered away from civilization. His only comings-and-goings were occasional trips to Lincoln on his beat-up bicycle, said neighbors, who invariably described him a harmless, eccentric loner.

While Kaczynski may have lived a Thoreau-like existence, presumably wanting nothing more than to be left alone, it was his apparent thirst for notoriety that began to steer investigators in his direction. Perhaps prompted by the World Trade Center bombing in New York City in February 1993, the Unabomber struck again in April of that year, ending a long hiatus. Within a three-day span, two bombs exploded on opposite sides of the country, injuring Charles Epstein, a geneticist at the University of California at San Francisco, and David Gerlertner, a computer-science professor at Yale University in New Haven, Conn.

Investigators’ frustrations deepened as the Unabomber’s activity picked up and grew more deadly over the next three years. In 1994, a mail bomb killed advertising executive Thomas Mosser at his North Caldwell, N.J., home. In April 1995, just a few days after the bombing of the Federal building in Oklahoma City, a bomb attributed to the Unabomber exploded again in Sacramento, killing timber-industry lobbyist Gilbert Murray. That June, a phoned-in bomb threat made to Los Angeles International Airport snarled air traffic nationwide and unnerved passengers.

Prosecutors apparently will have a strong forensic case against Kaczynski, judging from the mountain of physical evidence that investigators are said to have found in his remote cabin:

¶ Scrap metal and wood, which authorities say the Unabomber used to craft his meticulously constructed devices and made them hard to trace;

¶ Batteries and electrical wire that could be used for timing devices and detonators.

¶ Ten three-ring binders filled with writings and diagrams about constructing and concealing explosive devices, along with handwritten notes in English and Spanish describing how chemicals could be mixed to form explosive charges.

¶ Two manual typewriters that Federal agents believe were used by the suspect to type his “Unabomber Manifesto,” in which the writer railed against encroaching technology and urged humankind to return to “wild nature” or face extinction. The Unabomber sent the 35,000-word screed to The Washington Post and The New York Times, warning of more bombings unless it was published.

Despite fears that publishing the manifesto might inspire other criminals to extort publicity from the media, the newspapers published the manifesto in September 1995 in the hope that the treatise “might offer a clue to the Unabomber’s identity, if the right person saw it,” according to an unidentified source quoted by Newsweek magazine.

Someone did recognize the Unabomber’s ponderous prose style Kaczynski’s younger brother, David, who first approached the FBI through an intermediary in January, after becoming alarmed that themes in the manifesto were disturbingly similar to old letters he had found stored in an attic at his mother’s house. That was the tip out of thousands received, checked out and dead-ended over the years authorities needed to zero in on the suspect at long last.